1. Field of the Invention
This invention relates to an apparatus and method for the manufacture of a continuous sheet of glass wherein the glass is supported by a pool of molten metal while it is cooled and formed. More particularly, this invention relates to an improved apparatus and method for enhancing the rate at which glass is cooled as it advances along the surface of the molten metal during forming.
2. Description of the Prior Art
It is well known that molten glass may be delivered as a layer onto a pool of molten metal and then be cooled and formed while being advanced thereon to make a continuous sheet or ribbon of glass according to the teachings of Heal, U.S. Pat. No. 710,357; of Hitchcock, U.S. Pat. No. 789,911, of Pilkington; U.S. Pat. No. 3,083,551; or of Edge and Kunkle, U.S. Pat. No. 3,843,346. It also is well known that the cooling of glass during its advance along the surface of a pool of molten metal may be accomplished and controlled by the transfer of heat from the advancing glass to its supporting pool of molten metal and then through the bottom of the chamber or container holding the molten metal to coolers embedded in it or to external cooling surrounding it. For example, U.S. Pat. No. 3,645,713 illustrates a glass forming chamber having a refractory floor with passageways in it which communicate with openings in different regions of the chamber floor so that the liquid or molten metal can be circulated between those regions to regulate the temperature within the pool or bath of molten metal as desired. It is also known to employ a float forming chamber having bottom cooling beneath the casing of the chamber so heat transfer may be accomplished through the refractory liner and casing to the outside environment by maintaining a sufficiently low casing temperature due to the illustrated external cooling. U.S. Pat. No. 3,930,828 illustrates a glass forming chamber having coolers embedded in the refractory liner beneath a glass-supporting pool of molten metal. Heat transfer is established from the supported glass to the glass-supporting pool of molten metal and then through the overlying portion of refractory to the coolers embedded in the refractory liner.
The last-mentioned patent to Kunkle is particularly directed to a method and apparatus for controlling thermal conditions in a glass forming chamber in a way that permits the construction and operation of a relatively short glass forming chamber. However, experience indicates that sufficient cooling to suitably form glass in a short forming chamber on the order of one-fifth to one-tenth the length of a conventional float glass forming chamber requires heat transfer at rates which exceed the rates conveniently encountered when employing embedded coolers alone or when employing external bottom casing coolers alone. It would be possible to provide coolers simply submerged within a pool of molten metal, but such coolers would inherently act as barriers to the free circulation of the glass-supporting molten metal. Locations which may be ideally suited for cooler locations might not be the same locations which would be ideal for barrier locations. Therefore, it has been desired to develop a suitable apparatus for cooling glass by heat transfer through its supporting pool of molten metal which would provide heat transfer efficiencies approaching those for submerged coolers, yet providing for the free, unconstrained flow of pool of molten metal within the immediate region of influence of such coolers. The present invention is believed to provide such an apparatus.